1. Field of the Invention
The present invention relates to a substrate inspection method and substrate inspection device that are suitable for use in a silicon carbide (SiC) substrate constituting a nitride semiconductor device, and a method of manufacturing the nitride semiconductor device and an apparatus for manufacturing for the nitride semiconductor device using the substrate inspection method and the substrate inspection device.
2. Description of Related Art
At the moment, research on nitride semiconductors is actively progressing in the fields of optical devices and electronic devices because of advantages in physical characteristics.
In particular, in the electronic device field, the development of high electron mobility transistors (hereafter called “HEMT”) using nitride semiconductors is now in progress.
In the case of nitride semiconductor crystals, growing bulk single crystals is difficult because vapor pressure is high, so metal-organic chemical vapor deposition (hereafter called MOCVD) is widely used.
The MOCVD method is an epitaxial growth technology for forming a desired crystal layer on a substrate by sequentially supplying predetermined material gas onto the substrate under high temperature.
Recently in the electronic device field, a silicon carbide substrate (hereafter also called SiC substrate) is receiving attention. This is because the thermal conductivity of SiC is high, about 7-9 times the thermal conductivity of sapphire (Al2O3), which is generally used as the substrate material.
So now the technical development of HEMT, which can be obtained by growing nitride semiconductor crystals on the SiC substrate by the MOCVD method, and which has superb high frequency characteristics and high output characteristics, is on-going.
For example, according to the “Video Enhance System SMR-100” catalog from Nikon (as of August, 1994), the visual inspection of a manufactured HEMT can be performed by optical microscopic images.
However depositing a nitride semiconductor thin film on the SiC substrate by the abovementioned MOCVD method has the following problems.
First, in the SiC substrate as a crystal substrate, holes called micro-pipes, which penetrate from the front to the back of the substrate, exist as structural defects. The diameter of a micro-pipe differs depending on the growth conditions of single crystals, but is several μm to several tens μm in some cases.
Therefore if the film thickness of the nitride semiconductor thin film grown on the SiC substrate is normally 2 μm-3 μm, a part of the micro-pipes remain as defects after the thin film is grown.
In other words, the structural defects of the SiC substrate causes the generation of defects in the nitride semiconductor thin film on this substrate (this is called defect propagation).
Also in the SiC substrate, various structural defects exist in some cases, other than the abovementioned micro-pipes, such as macro defects (e.g. voids, grain boundaries), dislocations (e.g. spirals, blades, mosaics) and surface defects (surface polishing scratches, surface roughness). In these cases as well, a defect is propagated into the nitride semiconductor thin film deposited thereon.
HEMT, which has an SiC substrate with such structural defects, causes operation failures, which drops the reliability as a device.
However the inspection by the system shown in the abovementioned document is not the detection of structural defects but is merely a visual inspection for observing the surface of the device and dimensional errors, and it is impossible to inspect the quality of the device by detecting the abovementioned structural defects.
With the foregoing in view, it is an object of the present invention to provide a substrate inspection method and a substrate inspection device that can detect the structural defects generated inside the substrate, and a manufacturing method for a nitride semiconductor device and a manufacturing device for a nitride semiconductor device which use this substrate inspection method and substrate inspection device.